A 8-year-old female who prensented with left rib pain, hematuria and fever was admitted to our hospital, max temperature reached to 39.9℃, no chills and rash, she was given cefepime and azithromycin for one day, cefotaxime for 5 days,methylprednisolone for one day. On physical examination: the general condition was poor, eyelid and lower limbs edema, coarse respiratory sounds and auscultation of blisters of both lungs were noted, no other abnormal finding was present at that time. Laboratory findings were as follows: white blood cell count 6.32*109/L, neutrophil 0.48, lymphocyte 0.42, red blood cell count 3.40*1012/L, hemoglobin 93g/l, platelet count 48*10/L, urine revealed 363.69 red blood cells/hpf, protein 3+, 5.1 white blood cells/hpf, erythrocyte sedimentation rate(ESR) 135mm/h, C-reactive protein(CRP) 25.20mg/L, albumin 17.6g/L, total cholesterol 7.21mmol/L, her urinay protein 3.2g/24h.Activated partial thromboplastin time(APTT) 138.7s, direct antiglobulin test positive, ferritin 358.4ug/L, D-D 4937.00ug/L FDG 33.8ug/ml. Serum C3 0.92g/L(0.9-1.8), C4 0.17g/L(0.1-0.4), ANA:anti-SSA-60 ±,anti-nRNP/Sm+, homogeneous 1:3200 positive, dsDNA1:10 positive, anti-nucleosome antibody +, anti-mitochondrial M2 +, anti-cardiolipin IgM 12U/ml(0-10), anti-β 2-glycoprotein I 223RU/ml(0-20). Bone marrow biopsy: s econdary anemia, globular red blood cell accounted for 5.5%. However, respiratory pathogens, myocardial enzymes, mycoplasma pneumoniae/chlamydia antibodies, procalcitonin, folic acid, vitamin B12, reticulocytes, bacterial cultures of blood, stool, tuberculosis spots, Epstein Barr virus, cytomegalovirus, ANCA were all negative. Hematuria location: urine abnormal red blood cell 60%, urine uniform red blood cell 40%. Bronchoscope: inflammation of endobronchial membrane. Pulmonary CT: patchy high-density shadows in all lobes of the lungs, especially in the lower lobes of the lungs(Fig.1). Color doppler ultrasonography of the lower limbs ruled out deep venous thrombosis. Abdominal color ultrasound: abdominal effusion. Echocardiography: a kind of round moderate echo with a diameter of about 2.0cm can be seen at the bottom of the right atrium nearby the opening of the inferior vena cava. diagnosis: right atrial thrombus(Fig.2). Renal pathology: light microscopic:52 glomeruli were found in the renal tissue, there were 52 glomeruli in renal tissue, slight proliferation of mesangial cells and mesangial matrix, swelling and slight proliferation of segmental foot nuclear endothelial cells, slight thickening of glomerular basement membrane and large amount of furophilic protein deposition subepithelial cell. No microthrombus and crescent were seen, and a small amount of inflammatory cell infiltration dominated by neutrophils was found in some glomeruli. There was slight edema in the renal interstitium, and there was no renal tubular atrophy and obvious inflammatory cell infiltration and fibrosis. No obvious abnormality was found in the arterioles. Immunofluorescence study was positive for IgA, IgM, IgG, C3, C4, C1q deposited along the glomerular capillary wall and segmental mesangial area. The above features were consistent with membranous lupus nephritis with mesangial proliferative lupus nephritis(consistent with typeV+II lupus nephritis)(Fig.3,Fig.4). Nephrotic syndrome is a common disease in pediatrics, which is characterized by edema, massive proteinuria (>50mg/kg.24h), hypoproteinemia (<25g/l) and hypercholesterolemia (>5.7mmol/l), our patient was consistent with nephrotic syndrome[1]. Continued to track the etiology of nephrotic syndrome, the child had no family history of renal disease, we should pay attention to secondary factors, positive serology was positive for ANA and anti-dsDNA with low C3,platelets and hemoglobin were significantly lower than normal, but she had no rash, arthralgia, photosensitivity, oral ulcer, butterfly erythema, so a renal biopsy was performed, renal pathology suggested lupus nephritis, finally diagnosed as systemic lupus erythematosus, lupus nephritis. She was treated with pulse methylprednisolone for three days and IV diuretic with albumin, followed by oral steroids after three days 1mg/kg.d, with rapid resolution of edema. Anti-cardiolipin IgM 12U/ml, anti-β2-glycoprotein I 223R/ml, consisent with secondary anticardiolipin syndrome. What is the cause of the space occupying mass in the right atrium? At this point, as no clear etiological evidence was found, finally repeated echocardiography indicates that the nature of the right atrial mass is thrombus. The mass was reduced by anticoagulant therapy with heparin for two weeks. By three weeks, proteinuria came down to 1.0 g/day and by sixteen weeks he was in complete remission with <0.5g proteinuria. After six months follow-up, he remains in complete remission, but on 2.5 mg of prednisolone per day.